Running analysis for iPhone
Are you getting fitter? And why did today feel hard?
Cursans reads every run from your watch and every session from your plan, and tells you in plain words whether your training is working. No account: your runs stay on your iPhone.
Free iPhone beta · Apple Watch & Garmin · ready on day one
We only write to you about Cursans. Privacy policy
The problem
Your watch gives you numbers, not answers.
Pace, heart rate, a score. None of them says whether the training is working, or why a run felt hard.
- every run on one lineEach kind of run against its own kind
- a score every morningA note only when something changed
- heat, hills and bad sleep ignoredTested on your own runs
Am I getting fitter?
A trend you can believe, for each kind of run.
One line per kind of run, drawn so that one odd day can’t bend it. It turns green only when the change is bigger than your normal ups and downs.
Easy runs: 8% more speed per heartbeat in 24 weeks.
Efficiency · speed per heartbeat: more speed at the same heart rate is fitter
Weekly line, dashed trend. Along the bottom: how warm each week was. Made-up runner.
Progress in the guide ›Why did today feel hard?
Why a run felt the way it did.
After each run, one sentence says how it went, then each part with your own numbers. Over the months, heat, hills, sleep and more are tested on your own runs.
Reading a run in the guide ›After the run: Coach’s read
✦ Coach mode is on: each line says what it means. Tap it to turn it off. Made-up runs.
Over the months: What affects you
Heat costs this runner about 2.4% of efficiency per 10 °C. Wind doesn’t show.
A dot with its likely range against zero. It affects you only once your runs confirm it; it is said beside a run, never changing its colour.
Your week with Cursans
It speaks only when something is new.
Each note carries its moment, so you know when it applies. A normal day stays quiet.
Today in the guide ›-
Overnight
How you come in
After a hard session, one cell per night until your mornings are back to your usual. Silent when recovery is normal; it never tells you to rest.
After Tuesday’s intervals · usually back after 2 nights
Not back yet (55 bpm), within your usual 2 nights.
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Before the run
What today should look like
The heart rate your own recent runs expect at today’s pace, and how often that range has held.
Easy run at 5:30 /km · your runs expect 138–149 bpm
Inside the range: as expected
8 of the last 10 insideToday 27 °C at your usual hour; 6:00 is 4 °C cooler.
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After the run
Your intervals, rep by rep
Your coach wrote 6 × 800 m at 3:40 /km; your watch saw one run with laps. Each rep is read against its target: on target within ±2% (±3% under 800 m), slightly off up to twice that, clearly off beyond.
Try it · 6 × 800 m at 3:40 /km
Rep 1: 3:40 /km, on target.
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This week
When the week goes off
Can’t run today? Plan B finds the best day for the session and keeps your key sessions. Your plan itself stays with your coach or plan app.
Can’t run Tuesday’s intervals? · Week 52 km of 62, key sessions kept
Race season
Your marathon, explained.
Every marathon on one chart, km by km, and what limits the next one: your engine, or how much of it you hold for 42 km.
Races in the guide ›Compare · Marathon
Riverside 2026 held its efficiency longest: drift began at km 31.
| Race | Temp | Drift from | Finish |
|---|
What limits your marathon
Your race pace as a share of your engine, against what runners of your finish time usually hold (Smyth & Muniz-Pumares 2020; Joyner & Coyle 2008).
Built to be believed
Honest numbers, public rules.
- Day 1trends ready from the history you bring in
- 100%of runs get a type; when unsure, it asks you once
- 7conditions tested on your own runs
- 0accounts: your runs stay on your iPhone
| Topic | A typical running app | Cursans |
|---|---|---|
| Workout types | Whatever the watch called it | Every run typed; asked once when unsure |
| Trends | All runs on one line | Each kind against its own kind |
| “Improving” | Any line going up | Only beyond your normal ups and downs |
| Heat | Ignored, or quietly “corrected” | Judged as measured, your heat cost said beside |
| Your data | An account in the cloud | No account; stays on your iPhone |
Works with what you already use
Your plan stays where it is. Cursans shows whether it is working.
Watches
- Apple Watch, via Apple Health
- Garmin: Cursans view data field
- Garmin: Watch Copy, by cable
- Polar
- COROS
Plans
- Runna calendar
- TrainingPeaks calendar
- Garmin Connect calendar
- A coach’s session, pasted as written
Past runs
- Strava archive import
- Garmin and Polar account archives
- FIT, TCX and GPX files
For coaches
Your athlete’s training, read the way you wrote it.
An athlete sends you a report: every session read rep by rep against what you wrote, a trend per kind of run, and the conditions that affect them.
- A link, PDF or CSV, or a weekly link.
- Two consent switches, both off by default: overnight data and check-ins.
- The link holds only the report and ends after 30 days.
Who builds it
Cursans is built by Maikel Colli, a physician-scientist (MD-PhD in metabolism) and data scientist, and a runner. Every cut-off is public, the same on every screen, and cited.
How colours are decided ›Early access
Join the beta
Leave your email and we write when there is room in the beta, and at launch.
- Free during the beta
- iPhone, iOS 15 or later
- No Android yet
We use your email only to write to you about Cursans; to be removed, write to privacy@cursans.com.